Elevators are used in the oilfield industry for handling tubulars on drilling rigs. Some elevators include a body made up of two semi-circular portions that are hinged together and fitted around a tubular. A latch or connecting pin may be positioned opposite of the hinge to secure the semi-circular portions together. When disengaged, the latch or connecting pin allows for the semi-circular portions to be pivoted apart. Another type of elevator is in the shape of a horseshoe. Horseshoe-shaped elevators generally do not require disengaging a latch or connecting pin and pivoting the semi-circular portions apart to place the elevator around the tubular.
Horseshoe-shaped elevators are generally designed to support a tubular by lifting on the lower load face of a coupling that has been connected (“made up”) to the tubular. The coupling has a bore formed therethrough and female threads on an inner surface thereof. The coupling is designed to have two tubulars inserted into the bore through opposing ends of the coupling. Male threads on the tubulars may engage corresponding female threads of the coupling to join the tubulars together. As such, the outer diameter of the coupling is larger than the outer diameter of the tubulars. Thus, an upper surface of the elevator may contact a lower surface of the coupling, thereby allowing the elevator to support the weight of the tubular.
When no coupling is used, a lifting apparatus (often referred to as a “lift nubbin” or “lift plug”) is coupled to the tubular. The lifting apparatus includes a male threaded end that engages the female threads in the tubular. The lifting apparatus includes a flange portion on the outer diameter thereof that is larger than the outer diameter of the tubular. The elevator may contact a lower surface of the flange, thereby allowing the elevator to support the weight of the tubular. Attaching and removing lifting apparatuses, however, lengthens time taken to deploy each tubular into the well, as the lifting apparatus generally has to be installed and then removed before the tubular is made up to the next tubular.
As shown in FIGS. 19 and 20, a clamp-type elevator 1900 was created to avoid the use of lifting apparatuses. The clamp-type elevator 1900 includes tapered slips that are fitted with gripping inserts that are configured to radially-grip the outer diameter of the tubular. At least one of the slips 1911, 1912 is spring-biased upward, and at least one of the slips 1913, 1914 is pneumatically powered up and down. The operation of the clamp-type elevator 1900 involves laterally moving the elevator onto the tubular to be lifted. The front slip arms 1930, 1931 pivot about shafts 1940, 1941 into the deployed position shown in FIG. 19 and move the pneumatic slip(s) 1913, 1914 downward into initial engagement with the tubular 1920. As the tubular 1920 is lifted, the spring-biased slip(s) 1911, 1912 are drawn downward into increased radial gripping engagement with the tubular 1920.
In certain applications, the spring-biased slip(s) 1911, 1912 are drawn downward into contact with the tubular 1920 to be lifted prior to the pneumatic slips 1913, 1914 being energized. When this occurs, the spring-biased slip(s) 1911, 1912 may mechanically overload and fracture a mechanical stop that is designed to stop movement of the spring-biased slip(s) 1911, 1912 at the end of their downward stroke. Once this occurs, the slip becomes separated from the clamp-type elevator 1900 and becomes a dropped object. In some instances, this may cause the tubular 1920 to be dropped.
To reduce the run-in and trip-out time for tubulars, two, three, or more joints of tubulars are often pre-assembled into stands, which are then stored in racks, generally in a vertical orientation, for subsequent use. As noted above, lift nubbins are often used in the absence of drill collars, providing a shoulder for the elevator to engage and lift the tubular. As stands are being built, this presents two issues. First, each tubular requires a lift nubbin, and thus time is expended connecting and disconnecting lift nubbins. Further, the upper-most tubular supports the lower tubulars and is put into the rack (“racked-back”) with a lift nubbin at the top, and thus a rig operator is called upon to work at the top of the rack (which can be 40 feet or more above the rig floor) to disgengage the lift nubbin, or the lift nubbin may be left in place, which can require potentially hundreds of lift nubbins to be available on the rig.